As for conventional examples, document 1 (JP 2011-138716 A) discloses a power supply unit (lighting device), a light source unit (light source device), and an illuminating device.
According to the conventional examples disclosed in document 1, even when one selected from various types of light source units is electrically connected to the power supply unit, the power supply unit can supply, to the connected light source unit, power suitable for the connected light source unit.
Each light source unit includes a light source circuit and an identification circuit. The light source circuit is a series circuit of multiple light emitting diodes. The identification circuit is constituted by a resistor with a resistance associated with an electric property of the light source circuit. In each light source unit, one input end of the light source circuit and one end of the identification circuit (resistor) are connected to a plus input terminal, and the other input end of the light source circuit is connected to a minus input terminal, and the other end of the identification circuit is connected to a signal terminal.
The power supply unit includes a power supply circuit (e.g., DC-DC converter) supplying adjustable output, a type determiner, and a lighting controller. The power supply circuit is configured to apply a DC voltage between the two input terminals of the connected light source unit. The type determiner includes a dividing resistor to be connected in series with the identification circuit of the connected light source unit. The type determiner is configured to measure a resistance of the identification circuit (resistor) based on measurement of the voltage across the dividing resistor, and determine the type of the connected light source unit based on the measured resistance. The lighting controller is configured to determine a desired value of a load current in accordance with the determination result of the type determiner, and control the power supply circuit so that an output current has the desired value. Note that, electrical connection between the power supply unit and the light source unit is made by a connector.
In the conventional examples disclosed in document 1, the voltage applied across the light source circuit by the power supply circuit is also applied across the identification circuit, and thereby the number of wirings between the power supply unit and the light source unit is reduced.
Note that, in the conventional examples disclosed in document 1, the connector is used for interconnection between the power supply circuit and the light source unit, and hence a voltage drop may be caused by contact resistance of the connector in supplying power from the power supply circuit to the light source unit. Such a voltage drop is likely to be present on a signal to be detected in determining the type of the connected light source unit. This may cause the type determiner to make false determination with regard to the type of the connected light source unit, and as a result, incorrect output may be supplied to the connected light source unit (i.e., false operation may occur).